skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: GLOBULAR CLUSTER SYSTEMS OF SPIRAL AND S0 GALAXIES: RESULTS FROM WIYN IMAGING OF NGC 1023, NGC 1055, NGC 7332, AND NGC 7339

Abstract

We present results from a study of the globular cluster (GC) systems of four spiral and S0 galaxies imaged as part of an ongoing wide-field survey of the GC systems of giant galaxies. The target galaxies-the SB0 galaxy NGC 1023, the SBb galaxy NGC 1055, and an isolated pair comprised of the Sbc galaxy NGC 7339 and the S0 galaxy NGC 7332-were observed in BVR filters with the WIYN 3.5 m telescope and Minimosaic camera. For two of the galaxies, we combined the WIYN imaging with previously published data from the Hubble Space Telescope and the Keck Observatory to help characterize the GC distribution in the central few kiloparsecs. We determine the radial distribution (surface density of GCs versus projected radius) of each galaxy's GC system and use it to calculate the total number of GCs (N{sub GC}). We find N{sub GC} = 490 {+-} 30, 210 {+-} 40, 175 {+-} 15, and 75 {+-} 10 for NGC 1023, NGC 1055, NGC 7332, and NGC 7339, respectively. We also calculate the GC specific frequency (N{sub GC} normalized by host galaxy luminosity or mass) and find values typical of those of the other spiral and E/S0 galaxies in the survey. Themore » two lenticular galaxies have sufficient numbers of GC candidates for us to perform statistical tests for bimodality in the GC color distributions. We find evidence at a high confidence level (>95%) for two populations in the B - R distribution of the GC system of NGC 1023. We find weaker evidence for bimodality (>81% confidence) in the GC color distribution of NGC 7332. Finally, we identify eight GC candidates that may be associated with the Magellanic dwarf galaxy NGC 1023A, which is a satellite of NGC 1023.« less

Authors:
; ;  [1]
  1. Department of Astronomy, Indiana University, 727 East Third Street, Bloomington, IN 47405-7105 (United States)
Publication Date:
OSTI Identifier:
22089865
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (New York, N.Y. Online); Journal Volume: 144; Journal Issue: 4; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; CAMERAS; COLOR; DENSITY; GALAXIES; LUMINOSITY; MASS; SATELLITES; SPACE; SPATIAL DISTRIBUTION; STAR CLUSTERS; TELESCOPES

Citation Formats

Young, Michael D., Dowell, Jessica L., and Rhode, Katherine L., E-mail: youngmd@indiana.edu, E-mail: jlwind@astro.indiana.edu, E-mail: rhode@astro.indiana.edu. GLOBULAR CLUSTER SYSTEMS OF SPIRAL AND S0 GALAXIES: RESULTS FROM WIYN IMAGING OF NGC 1023, NGC 1055, NGC 7332, AND NGC 7339. United States: N. p., 2012. Web. doi:10.1088/0004-6256/144/4/103.
Young, Michael D., Dowell, Jessica L., & Rhode, Katherine L., E-mail: youngmd@indiana.edu, E-mail: jlwind@astro.indiana.edu, E-mail: rhode@astro.indiana.edu. GLOBULAR CLUSTER SYSTEMS OF SPIRAL AND S0 GALAXIES: RESULTS FROM WIYN IMAGING OF NGC 1023, NGC 1055, NGC 7332, AND NGC 7339. United States. doi:10.1088/0004-6256/144/4/103.
Young, Michael D., Dowell, Jessica L., and Rhode, Katherine L., E-mail: youngmd@indiana.edu, E-mail: jlwind@astro.indiana.edu, E-mail: rhode@astro.indiana.edu. Mon . "GLOBULAR CLUSTER SYSTEMS OF SPIRAL AND S0 GALAXIES: RESULTS FROM WIYN IMAGING OF NGC 1023, NGC 1055, NGC 7332, AND NGC 7339". United States. doi:10.1088/0004-6256/144/4/103.
@article{osti_22089865,
title = {GLOBULAR CLUSTER SYSTEMS OF SPIRAL AND S0 GALAXIES: RESULTS FROM WIYN IMAGING OF NGC 1023, NGC 1055, NGC 7332, AND NGC 7339},
author = {Young, Michael D. and Dowell, Jessica L. and Rhode, Katherine L., E-mail: youngmd@indiana.edu, E-mail: jlwind@astro.indiana.edu, E-mail: rhode@astro.indiana.edu},
abstractNote = {We present results from a study of the globular cluster (GC) systems of four spiral and S0 galaxies imaged as part of an ongoing wide-field survey of the GC systems of giant galaxies. The target galaxies-the SB0 galaxy NGC 1023, the SBb galaxy NGC 1055, and an isolated pair comprised of the Sbc galaxy NGC 7339 and the S0 galaxy NGC 7332-were observed in BVR filters with the WIYN 3.5 m telescope and Minimosaic camera. For two of the galaxies, we combined the WIYN imaging with previously published data from the Hubble Space Telescope and the Keck Observatory to help characterize the GC distribution in the central few kiloparsecs. We determine the radial distribution (surface density of GCs versus projected radius) of each galaxy's GC system and use it to calculate the total number of GCs (N{sub GC}). We find N{sub GC} = 490 {+-} 30, 210 {+-} 40, 175 {+-} 15, and 75 {+-} 10 for NGC 1023, NGC 1055, NGC 7332, and NGC 7339, respectively. We also calculate the GC specific frequency (N{sub GC} normalized by host galaxy luminosity or mass) and find values typical of those of the other spiral and E/S0 galaxies in the survey. The two lenticular galaxies have sufficient numbers of GC candidates for us to perform statistical tests for bimodality in the GC color distributions. We find evidence at a high confidence level (>95%) for two populations in the B - R distribution of the GC system of NGC 1023. We find weaker evidence for bimodality (>81% confidence) in the GC color distribution of NGC 7332. Finally, we identify eight GC candidates that may be associated with the Magellanic dwarf galaxy NGC 1023A, which is a satellite of NGC 1023.},
doi = {10.1088/0004-6256/144/4/103},
journal = {Astronomical Journal (New York, N.Y. Online)},
number = 4,
volume = 144,
place = {United States},
year = {Mon Oct 01 00:00:00 EDT 2012},
month = {Mon Oct 01 00:00:00 EDT 2012}
}
  • We present results from a WIYN 3.5 m telescope imaging study of the globular cluster (GC) systems of the edge-on spiral galaxies NGC 891 and NGC 4013. We used the 10' x 10' Minimosaic Imager to observe the galaxies in BVR filters to projected radii of {approx}20 kpc from the galaxy centers. We combined the WIYN data with archival and published data from the WFPC2 and AdvancedCameraforSurveys on the Hubble Space Telescope (HST) to assess the contamination level of the WIYN GC candidate sample and to follow the GC systems further in toward the galaxies' centers. We constructed radial distributionsmore » for the GC systems using both the WIYN and HST data. The GC systems of NGC 891 and NGC 4013 extend to 9 {+-} 3 kpc and 14 {+-} 5 kpc, respectively, before falling off to undetectable levels in our images. We use the radial distributions to calculate global values for the total number (N{sub GC}) and specific frequencies (S{sub N} and T) of GCs. NGC 4013 has N{sub GC} = 140 {+-} 20, S{sub N} = 1.0 {+-} 0.2, and T = 1.9 {+-} 0.5; our N{sub GC} value is {approx}40% smaller than a previous determination from the literature. The HST data were especially useful for NGC 891 because the GC system is concentrated toward the plane of the galaxy and was only weakly detected in our WIYN images. Although NGC 891 is thought to resemble the Milky Way in terms of its overall properties, it has only half as many GCs, with N{sub GC}= 70 {+-} 20, S{sub N} = 0.3 {+-} 0.1, and T = 0.6 {+-} 0.3. We also calculate the galaxy-mass-normalized number of blue (metal-poor) GCs in NGC 891 and NGC 4013 and find that they fall along a general trend of increasing specific frequency of blue GCs with increasing galaxy mass. Given currently available resources, the optimal method for studying the global properties of extragalactic GC systems is to combine HST data with wide-field, ground-based imaging with good resolution. The results here demonstrate the advantage gained by using both methods when possible.« less
  • In this paper, we present the results of a wide-field imaging study of the globular cluster (GC) system of the field S0 galaxy NGC 7457. To derive the global properties of the GC system, we obtained deep BVR images with the WIYN 3.5 m telescope and Minimosaic Imager and studied the GC population of NGC 7457 to a projected radius of {approx}30 kpc. Our ground-based data were combined with archival and published Hubble Space Telescope data to probe the properties of the GC system close to the galaxy center and reduce contamination in the GC candidate sample from foreground starsmore » and background galaxies. We performed surface photometry of NGC 7457 and compared the galaxy's surface brightness profile with the surface density profile of the GC system. The profiles have similar shapes in the inner 1' (3.9 kpc), but the GC system profile appears to flatten relative to the galaxy light at larger radii. The GC system of NGC 7457 is noticeably elliptical in our images; we measure {epsilon} = 0.66 {+-} 0.14 for the GC distribution, which is consistent with our measured ellipticity of the galaxy light. We integrated the radial surface density profile of the GC system to derive a total number of GCs, N{sub GC} = 210 {+-} 30. The GC specific frequencies normalized by the galaxy luminosity and mass are S{sub N} = 3.1 {+-} 0.7 and T = 4.8 {+-} 1.1, respectively. Comparing the derived GC system properties and other empirical data for NGC 7457 to S0 formation scenarios suggests that this field S0 galaxy may have formed in an unequal-mass merger.« less
  • We present new metallicity estimates for globular cluster (GC) candidates in the Sd spiral NGC 300, one of the nearest spiral galaxies outside the Local Group. We have obtained optical spectroscopy for 44 Sculptor Group GC candidates with the Boller and Chivens (B and C) spectrograph on the Baade Telescope at Las Campanas Observatory. There are two GCs in NGC 253 and 12 objects in NGC 300 with globular-cluster-like spectral features, nine of which have radial velocities above 0 km s{sup -1}. The remaining three, due to their radial velocities being below the expected 95% confidence limit for velocities ofmore » NGC 300 halo objects, are flagged as possible foreground stars. The non-cluster-like candidates included 13 stars, 15 galaxies, and an H II region. One GC, four galaxies, two stars, and the H II region from our sample were identified in archival Hubble Space Telescope images. For the GCs, we measure spectral indices and estimate metallicities using an empirical calibration based on Milky Way GCs. The GCs of NGC 300 appear similar to those of the Milky Way. Excluding possible stars and including clusters from the literature, the GC system (GCS) has a velocity dispersion of 68 km s{sup -1} and has no clear evidence of rotation. The mean metallicity for our full cluster sample plus one literature object is [Fe/H] = -0.94, lying above the relationship between mean GC metallicity and overall galaxy luminosity. Excluding the three low-velocity candidates, we obtain a mean [Fe/H] = -0.98, still higher than expected, raising the possibility of significant foreground star contamination even in this sample. Visual confirmation of genuine GCs using high-resolution space-based imagery could greatly reduce the potential problem of interlopers in small samples of GCSs in low-radial-velocity galaxies.« less
  • High-dispersion spectra of 89 potential members of the old, super-metal-rich open cluster, NGC 6253, have been obtained with the HYDRA multi-object spectrograph. Based upon radial-velocity measurements alone, 47 stars at the turnoff of the cluster color-magnitude diagram (CMD) and 18 giants are identified as potential members. Five turnoff stars exhibit evidence of binarity while proper-motion data eliminate two of the dwarfs as members. The mean cluster radial velocity from probable single-star members is -29.4 {+-} 1.3 km s{sup -1} (sd). A discussion of the current estimates for the cluster reddening, derived independently of potential issues with the BV cluster photometry,more » lead to an adopted reddening of E(B - V) = 0.22 {+-} 0.04. From equivalent width analyses of 38 probable single-star members near the CMD turnoff, the weighted average abundances are found to be [Fe/H] = +0.43 {+-} 0.01, [Ni/H] = +0.53 {+-} 0.02, and [Si/H] = +0.43{sup 0.03}{sub 0.04}, where the errors refer to the standard errors of the weighted mean. Weak evidence is found for a possible decline in metallicity with increasing luminosity among stars at the turnoff. We discuss the possibility that our turnoff stars have been affected by microscopic diffusion. For 15 probable single-star members among the giants, spectrum synthesis leads to abundances of +0.46{sup 0.02}{sub 0.03} for [Fe/H]. While NGC 6253 is less than half the age of NGC 6791, it is at least as metal-rich and, within the uncertainties, exhibits the same general abundance pattern as that typified by super-metal-rich dwarfs of the galactic bulge.« less
  • We present a spectroscopic analysis of the metallicities, ages, and alpha-elements of the globular clusters (GCs) in the giant elliptical galaxy (gE) NGC 4636 in the Virgo Cluster. Line indices of the GCs are measured from the integrated spectra obtained with Faint Object Camera and Spectrograph on the Subaru 8.2 m Telescope. We derive [Fe/H] values of 59 GCs based on the Brodie and Huchra method, and [Z/H], age, and [{alpha}/Fe] values of 33 GCs from the comparison of the Lick line indices with single stellar population models. The metallicity distribution of NGC 4636 GCs shows a hint of amore » bimodality with two peaks at [Fe/H] = -1.23({sigma} = 0.32) and -0.35({sigma} = 0.19). The age spread is large from 2 Gyr to 15 Gyr and the fraction of young GCs with age <5 Gyr is about 27%. The [{alpha}/Fe] of the GCs shows a broad distribution with a mean value [{alpha}/Fe] Almost-Equal-To 0.14 dex. The dependence of these chemical properties on the galactocentric radius is weak. We also derive the metallicities, ages, and [{alpha}/Fe] values for the GCs in other nearby gEs (M87, M49, M60, NGC 5128, NGC 1399, and NGC 1407) from the line index data in the literature using the same methods as used for NGC 4636 GCs. The metallicity distribution of GCs in the combined sample of seven gEs including NGC 4636 is found to be bimodal, supported by the KMM test with a significance level of >99.9%. All these gEs harbor some young GCs with ages less than 5 Gyr. The mean age of the metal-rich GCs ([Fe/H] >-0.9) is about 3 Gyr younger than that of the metal-poor GCs. The mean value of [{alpha}/Fe] of the gE GCs is smaller than that of the Milky Way GCs. We discuss these results in the context of GC formation in gEs.« less